The present invention relates to a process for the combustion of a high viscosity liquid fuel by means of an oxygenated gas, in particular one that can be used for a steam boiler.
Steam boilers may use various types of fuels: gaseous fuels (natural gas), liquid fuels (heavy fuel oils) or solid fuels (pulverized coal). The oxidizer used on the other hand is at the present time systematically air.
Although it is widely known to use pure or concentrated oxygen in the combustion of any type of fuel in many industries (glass, metallurgy, etc.) this is not used at all in the field of energy production using steam boilers for two main reasons: on the one hand, for an economic reason (cost of oxygen as an oxidant) and on the other hand, for a technical reason which is the problem of transferring heat between the oxygen flame and the steam. However, this type of combustion with oxygen becomes economically attractive since it makes it possible to capture easily, and at moderate cost, the CO2 contained in the fumes, which is a major objective within the environmental context. This transfer problem stems from an absence of nitrogen ballast present in the air, the flame obtained by combustion of fuel and oxygen being shorter and hotter than a flame obtained by the combustion of fuel and air. The heat transfer zone is more restricted and the local heat flux levels may reach values of 600 to 1000 kW/m2, which means higher tube temperatures and therefore problems with materials (corrosion).
In order to get round this problem of high localized flux levels, the solution generally selected is flue gas recycling. This solution makes it possible to replace nitrogen in the air with a high volume of recycled flue gases which once again gives the flame characteristics close to those of an air flame. Obviously this solution is not the optimum one since this flue gas recirculation involves adding a supplementary circuit and a blower. It may also present erosion and corrosion problems.
In addition, in the current context of the oilfield production, the use of liquid fuels and in particular high viscosity liquid fuels (called heavy residues) is becoming increasingly frequent for combustion in boilers.